Ignition Coil

The present application is a continuation application of International Application No. PCT/JP2024/008306 filed on March 5, 2024, which is based on and claims priority from Japanese Patent Application No. 2023-081022 filed on May 16, 2023. The entire contents of these applications are incorporated by reference into the present application.

The present disclosure relates to ignition coils for use in ignition apparatuses of internal combustion engines.

Ignition apparatuses provided in internal combustion engines generally include an ignition coil for applying a high voltage to an ignition plug facing a combustion chamber. In recent years, highly efficient internal combustion engines have been required to be more compact in order to improve fuel efficiency. Moreover, the internal structures of cylinder heads to which ignition apparatuses are provided have become increasingly complex; and there are increasing constraints on those parts of cylinder heads to which ignition apparatuses are assembled. Therefore, investigations have been conducted to form plug holes, in which ignition plugs are placed, in a bent shape and thereby make the assembly structures of ignition coils more compact.

In this case, it is required to configure joint parts of ignition coils, which are fitted to ignition plugs, with flexible one-piece molded products that are formed, for example, of rubber and to mount the joint parts in a bent state inside the plug holes. For example, Japanese Patent No. JP 4267042 B2 discloses an ignition coil apparatus for an internal combustion engine which includes a cylindrical plug boot that serves as a joint part. The plug boot, which is electrically insulative and flexible, has formed therein a thin wall part that is opposed to a bend of a plug hole. The thin wall part can be easily bent when an ignition plug is inserted into the plug boot in the plug hole that is bent in the middle and has a constant diameter. Furthermore, a radially-protruding guard part is provided at a distal end of the plug boot to facilitate the alignment of central axes of the plug boot and the ignition plug and thereby improve the insertability.

When mounting an ignition apparatus in a bent plug hole, it is necessary to insert a tool into the plug hole. Therefore, in practice, it is difficult to set the plug hole diameter to be constant as disclosed in the aforementioned patent document; and the inner diameter of the plug hole on the plug hole entrance side of the bend is generally greater than that on the ignition plug side of the bend. In this case, if the entire joint part is formed of an elastic material, local compression or deflection is likely to occur due to the compressive force applied during the insertion of the ignition plug. Therefore, it is difficult to mount the joint part while simultaneously suppressing axial misalignment at the bend of the plug hole and on both the distal and proximal sides thereof. Moreover, with the shape of the joint part having a thin wall part as disclosed in the aforementioned patent document, if the thin wall part is brought into contact with the bend of the plug hole by, for example, axial misalignment, wear may occur due to vibration or the like after the ignition coil has been mounted to an engine; thus, the withstand voltage of the ignition coil may be lowered.

The present disclosure has been accomplished in view of the above problems.

According to the present disclosure, there is provided an ignition coil configured to supply a high voltage to an ignition plug arranged in a plug hole having a bend, the ignition coil comprising:

a coil main body part configured to be arranged at a proximal-side entrance part of the plug hole, the proximal-side entrance part having an inner diameter greater than that of the bend; and

a joint part formed of a tubular elastic body that is bendable and deformable, the join part having a proximal end mounted to the coil main body part and a distal end to be mounted to the ignition plug,

wherein:

the joint part has a plurality of first ribs formed on an outer circumferential surface of a main tubular portion of the joint part, each of the first ribs extending along an axis of the joint part, the main tubular portion having a part thereof to be opposed to the bend of the plug hole;

the first ribs are arranged continuously, on both a distal side and a proximal side of the part of the main tubular portion which is to be opposed to the bend of the plug hole, toward both a distal end and a proximal end of the main tubular portion;

the joint part also has a plurality of second ribs formed on an outer circumferential surface of a proximal-side tubular portion of the joint part, each of the second ribs also extending along the axis of the joint part, the proximal-side tubular portion being located on a proximal side of the main tubular portion; and

d 1 when viewed along the axis of the joint part, a maximum valueof a first rib diameter, which is represented by the diameter of an imaginary circumscribing

d d 2 1 circle having its center located on the axis and circumscribing tips of the first ribs, and a maximum value d2 of a second rib diameter, which is represented by the diameter of an imaginary circumscribing circle having its center located on the axis and circumscribing tips of the second ribs, satisfy the relationship of>.

With the above configuration of the ignition coil according to the present disclosure, the rigidity of the joint part is improved by the first ribs formed on the main tubular portion of the joint part and the second ribs formed on the proximal-side tubular portion of the joint part. Moreover, with the first and second ribs, each of which extends along the axis of the joint part, serving as guides, the insertability of the joint part into the plug hole is improved. Consequently, the main tubular portion can be bent and deformed along the shape of the bent plug hole while suppressing axial misalignment; and the first ribs are arranged at a location facing the bend of the plug hole and coaxially with the plug hole. Furthermore, on the side of the proximal-side entrance part whose inner diameter is greater than that of the bend, there is arranged the proximal-side tubular portion on which the second ribs, whose maximum diameter is greater than that of the first ribs, are formed. Consequently, it becomes possible to suppress axial misalignment during the insertion of the joint part into the plug hole and displacement due to vibration or the like, thereby suppressing deterioration of characteristics due to wear.

In summary, according to the present disclosure, it becomes possible to provide the ignition coil which, when being mounted into the bent plug hole, can suppress axial misalignment while maintaining the insertability of the joint part, thereby improving the assemblability and wear resistance.

1 6 FIGS.to 1 FIG. 1 1 1 11 2 2 An embodiment embodying an ignition coil according to the present disclosure will be described with reference to. As shown in, an ignition coilis electrically connected to an ignition plug P provided in an internal combustion engine such as a vehicle engine, and is used to supply a high voltage to the ignition plug P. The ignition plug P is arranged in a plug hole H having a bend H. The ignition coilincludes a coil main body partarranged at a proximal-side entrance part Hof the plug hole H, and a joint part.

1 1 2 1 2 2 11 The plug hole H, which is formed in a cylinder head E, has a bent shape with the bend Hformed in the middle. The proximal-side entrance part Hof the plug hole H has an inner diameter greater than that of the bend H. The joint partis formed of a tubular elastic body that is bendable and deformable. In the plug hole H, the joint partis mounted at its proximal end to the coil main body part, and is mounted at its distal end to the ignition plug P.

2 11 2 1 1 1 1 2 2 FIG. The proximal side is the plug hole entrance side when the joint partis inserted into the plug hole H and mounted to the ignition plug P in the extending direction of the bent plug hole H as shown in, and is the side where the coil main body partis arranged. The distal side is the opposite side to the proximal side, and is the side where the ignition plug P is arranged. In the bent plug hole H, the axis Lon the proximal side of the bend Hdoes not coincide with the axis Lon the distal side of the bend H; therefore, the extending direction of the plug hole H, which is the direction along the axes Land L, also changes.

1 FIG. 3 FIG. 2 21 22 21 21 31 2 22 32 2 31 32 2 In the assembled state shown in, the joint parthas a main tubular portionincluding a portion facing the bend H1 of the plug hole H, and a proximal-side tubular portionlocated on the proximal side of the main tubular portion. As shown in, on an outer circumferential surface of the main tubular portion, there are formed a plurality of first ribseach extending along the axis L of the joint part. On the other hand, on an outer circumferential surface of the proximal-side tubular portion, there are formed a plurality of second ribseach extending along the axis L of the joint part. The first ribsand the second ribseach protrude in a direction perpendicular to the axis L, i.e., protrude outward in a radial direction X of the joint part.

4 FIG. 21 1 1 21 31 22 2 2 22 32 2 2 1 2 22 21 c c d d d Moreover, as shown in, when viewed in a direction along the axis L, a first rib diameter in the main tubular portionis represented by the diameter of an imaginary circumscribing circle Cthat has its centerlocated on the axis of the main tubular portionand circumscribes the tips of the first ribs; and a second rib diameter in the proximal-side tubular portionis represented by the diameter of an imaginary circumscribing circle Cthat has its centerlocated on the axis of the proximal-side tubular portionand circumscribes the tips of the second ribs. Furthermore, the maximum value d1 of the first rib diameter and the maximum valueof the second rib diameter satisfy the relationship of>. That is, the joint partis configured so that the maximum outer diameter of the proximal-side tubular portionis greater than the maximum outer diameter of the main tubular portion.

2 1 31 32 31 32 2 1 1 31 1 32 31 1 With the above configuration, during the insertion of the joint partof the ignition coilinto the bent plug hole H, the first ribsand the second ribsserve as guides, thereby improving the insertability. Moreover, with the first ribsand the second ribs, the rigidity of the joint partof the ignition coilis improved, thereby making it possible to assemble the ignition coilto the plug hole H while suppressing axial misalignment. In addition, the first ribsare arranged to face the bend Hof the plug hole H, while the second ribs, whose maximum outer diameter is greater than that of the first ribs, are arranged on the plug hole entrance side where the inner diameter of the plug hole H is greater than that at the bend H.

31 2 1 21 31 31 1 2 Specifically, the first ribsmay be arranged continuously on both the distal and proximal sides of that portion of the joint partwhich faces the bend Hof the plug hole H. In this case, when the main tubular portionincluding the first ribsis bent and deformed according to the bent shape of the plug hole H, the first ribsare located astride the bend Hof the plug hole H, thereby enhancing the effects of suppressing axial misalignment during the insertion of the joint partinto the plug hole H and displacement due to vibration or the like.

32 2 2 2 11 2 2 On the other hand, the second ribsmay be arranged continuously from the proximal side to the distal side, facing a proximal-side end part of the plug hole H which includes the proximal-side entrance part H. Consequently, the axial rigidity of the joint parton the proximal side is improved, thereby enhancing the effects of suppressing axial misalignment during the insertion of the joint partinto the plug hole H and displacement due to vibration or the like. Moreover, when assembling the coil main body partto the plug hole H after the insertion of the joint partinto the plug hole H, axial misalignment is suppressed, thereby improving the assemblability. The shape of the joint partwill be described in more detail later.

1 1 2 1 1 2 1 21 1 22 1 21 22 1 1 1 2 FIG. 1 FIG. 1 2 FIGS.and Next, the assembly structure of the ignition coilto the plug hole H will be described in detail.shows the state of the ignition coilbefore the joint partis bent during the assembly of the ignition coilto the plug hole H. On the other hand,shows the state of the ignition coilafter being assembled to the plug hole H. As shown in, the plug hole H, in which the joint partof the ignition coilis accommodated, has a distal-side half part Hlocated on the distal side of the bend Hand a proximal-side half part Hlocated on the proximal side of the bend H. The distal-side half part His a circular hole having a substantially constant diameter and extending to a mounting portion of the ignition plug P. On the other hand, the proximal-side half part His a tapered hole whose diameter gradually increases from the bend Htoward the proximal side. The bend His provided at an intermediate position in the extending direction of the plug hole H. It should be noted that the bend Hmay be located either distalward or proximalward from the position thereof shown in the drawings.

1 1 21 2 22 2 11 1 22 1 1 2 22 22 21 1 1 FIG. 1 2 FIGS.and The plug hole H is formed at a predetermined position in the cylinder head Efor each cylinder of the engine. The axis Lof the distal-side half part His inclined with respect to the axis Lof the proximal-side half part H. The axis Lextends in a direction perpendicular to a first surface Eof the cylinder head Ewhere the proximal-side half part Hopens. The bending angle of the bend His represented by the inclination angle θ of the axis Lwith respect to the axis L(see), which is equal to the taper angle of the proximal-side half part Hin the present embodiment. That is, in the left half of the cross section shown in, the inner circumferential surface of the proximal-side half part Hcontinues from the inner circumferential surface of the distal-side half part Hwithout bending; in contrast, in the right half of the cross section, the bend His formed.

1 21 2 2 22 2 1 2 21 1 22 21 31 32 21 22 21 21 22 1 22 22 2 2 FIG. Moreover, a first inner diameter Dof the plug hole H at the distal-side half part Hand a second inner diameter Dof the plug hole H at the proximal-side entrance part Hthat opens on the proximal side of the proximal-side half part Hsatisfy the relationship of D> D(see). Therefore, the joint parthas the main tubular portionlocated astride the bend Hof the plug hole H and the proximal-side tubular portionlocated on the proximal side of the main tubular portion. The first ribsand the second ribsare provided respectively in the main tubular portionand the proximal-side tubular portion. The main tubular portionis opposed to both a portion of the distal-side half part Hof the plug hole H and a portion of the proximal-side half part Hof the plug hole H which are continuous with each other with the bend Hinterposed therebetween. On the other hand, the proximal-side tubular portionis opposed to a portion of the proximal-side half part Hof the plug hole H which includes the proximal-side entrance part H.

1 FIG. 2 FIG. 3 21 3 21 1 2 1 3 1 4 1 5 4 3 As shown in, the ignition plug P is arranged so as to close a distal end hole Hthat continues from the distal-side half part H. The distal end hole His a circular hole having a substantially constant diameter less than the diameter of the distal-side half part H. The ignition plug P has its distal end arranged so as to face a combustion chamber (not shown) of the engine. The ignition plug P has an insulator P, a head terminal P(see) protruding from the insulator Ptoward the proximal side, a housing Pthat holds the insulator Ptherein, a center electrode Pprotruding from the insulator Ptoward the distal side, and a ground electrode Popposed to the center electrode P. Moreover, the ignition plug P also has a threaded portion formed in an outer circumferential surface of the housing P, and a hexagonal portion formed on the proximal side of the threaded portion for engaging with a tool. The ignition plug P is fastened and fixed in the plug hole H.

3 5 FIGS.to 5 FIG. 2 2 2 23 21 1 2 24 21 22 23 24 23 24 2 3 23 4 24 4 3 d d d d As shown in, the joint partis constituted of a tubular one-piece molded product that is formed entirely of an electrically-insulative elastic material such as rubber. The joint partis configured so that it can be freely elastically deformed according to the shape of the plug hole H and be held in a bent state. The joint parthas a straight-shaped distal-side tubular portionformed on the distal side of the main tubular portionand fitted onto a head portion of the insulator Pof the ignition plug P. The joint partalso has a straight-shaped intermediate tubular portionformed between the main tubular portionand the proximal-side tubular portion. Each of the distal-side tubular portionand the intermediate tubular portionhas a flat cylindrical outer circumferential surface with no ribs formed thereon, and has a substantially constant outer diameter. Moreover, each of the distal-side tubular portionand the intermediate tubular portionhas a smaller thickness and a lower rigidity and thus can be more easily elastically deformed than those portions of the joint partwhich have ribs formed thereon. Furthermore, the outer diameterof the distal-side tubular portionand the outer diameterof the intermediate tubular portionsatisfy the relationship of>(see).

2 FIG. 20 2 4 11 4 4 23 23 1 1 4 2 23 1 23 As shown in, in a cylindrical holethat axially penetrates the joint part, there is accommodated an electroconductive memberthat electrically connects the coil main body partand the ignition plug P. In the present embodiment, the electroconductive memberis constituted of a spring that is elastically deformable in the axial direction. The electroconductive memberhas its distal end located inside the distal-side tubular portion. The distal-side tubular portionhas the insulator Pinserted thereinto from the proximal end of the insulator P, thereby bringing the electroconductive memberinto abutment with the head terminal P. The axial length of the distal-side tubular portionmay be suitably set so as to obtain a desired fitting dimension, taking into account the amount of compressive deformation when the head portion of the insulator Pis inserted into the distal-side tubular portion.

4 FIG. 3 FIG. 31 21 2 31 21 2 31 31 2 31 21 24 23 As shown in, the first ribs, each of which has the shape of a protrusion protruding outward in the radial direction X, are formed respectively at a plurality of locations on the outer circumferential surface of the main tubular portionof the joint part. More particularly, in the present embodiment, eight first ribsare formed respectively at eight locations on the outer circumferential surface of the main tubular portionof the joint part. The first ribseach have a substantially trapezoidal cross-sectional shape, protrude in a radial fashion, and together form a gear-like external shape. The first ribsextend parallel to each other along the axis L of the joint part. Moreover, the first ribsare formed over the entire length from the proximal side to the distal side of the main tubular portion, i.e., from the distal end position of the intermediate tubular portionto the proximal end position of the distal-side tubular portion(see).

3 FIG. 4 FIG. 5 FIG. 31 311 21 1 21 1 311 31 23 11 3 23 1 11 3 21 311 31 1 d d d d d d d As shown in, each of the first ribshas, at a distal end thereof, a tapered portionthat slopes downward toward the distal side. Therefore, in a distal end part of the main tubular portion, the first rib diameter, which is the diameter of the imaginary circumscribing circle Cshown in, gradually decreases toward the distal side. In the main tubular portionexcluding the distal end part thereof, the first rib diameter is substantially constant and has the maximum value. Moreover, distal ends of the tapered portionsof the first ribsare connected with the distal-side tubular portion. Therefore, the minimum valueof the first rib diameter is greater than or equal to the outer diameterof the distal-side tubular portionshown in. That is, the following relationship is satisfied:>≥. In the distal end part of the main tubular portionwhere the tapered portionsof the first ribsare formed, the first rib diameter increases toward the proximal side, approaching the maximum value.

31 21 311 21 As above, each of the first ribsof the main tubular portionhas the tapered portionformed at the distal end thereof, so that the main tubular portionas a whole has a tapered shape that narrows toward the distal side, thereby improving the insertability.

21 1 24 4 24 1 3 23 4 1 11 3 21 24 21 31 21 31 21 24 21 31 d d d d d d d d 5 FIG. The main tubular portionis connected, on the proximal side thereof and with the first rib diameter kept substantially constant at the maximum value, with the intermediate tubular portionthat has a substantially constant diameter. Moreover, the outer diameterof the intermediate tubular portionshown inis greater than or equal to the maximum valueof the first rib diameter, and is thus greater than the outer diameterof the distal-side tubular portion(i.e.,≥>≥). To achieve the above relationship, in an end part of the main tubular portionon the intermediate tubular portionside, those portions of the main tubular portionwhich are located between the circumferentially adjacent first ribs(i.e., those portions of the main tubular portionwhere no first ribsare formed) are formed so as to gradually become thicker toward the proximal side and protrude radially outward. Consequently, in the end part of the main tubular portionon the intermediate tubular portionside, the rigidity of the main tubular portionis improved and the protruding height of the first ribsdecreases toward the proximal side.

31 21 31 31 1 31 1 21 1 1 2 FIG. 4 FIG. d It is preferable that the first ribsbe evenly arranged at substantially equal intervals in the circumferential direction on the outer circumferential surface of the main tubular portion. The protruding ends of the first ribsface the inner circumferential surface of the plug hole H, which is located outside the first ribsin the radial direction X, through a gap formed therebetween. The larger the gap, the more the insertability is improved. However, there is a risk of axial misalignment. Therefore, it is preferable that in the vicinity and on the distal side of the bend H, the inner circumferential surface of the plug hole H and the first ribsbe located close to each other with a slight gap, which is within a range that does not impair the insertability, formed therebetween. In this case, a first inner diameter D(see) in the distal-side half part Hof the plug hole H and the maximum value d1 (see) of the first rib diameter satisfy the relationship of D>.

21 31 1 23 22 31 2 2 23 2 31 31 1 25 2 2 2 25 23 25 25 The axial length of the main tubular portionon which the first ribsare arranged is not necessarily limited, but may be suitably set depending on the position of the bend Hin the plug hole H. Specifically, taking into account the length of the distal-side tubular portionmounted to the ignition plug P, the length of the proximal-side tubular portionand the like, the proximal end position of the first ribsmay be set to, for example, a position within a range of 30% to 80% of the length of the joint partfrom the distal end position of the joint part(i.e., the distal end position of the distal-side tubular portion). Moreover, in terms of improving the rigidity of the joint part, it is preferable that the axial length of the first ribsbe set as long as possible within the above range so that the proximal end position of the first ribsis on the proximal side of the bend Hof the plug hole H. In addition, a seal partis generally provided, on the proximal side of the joint part, integrally with the joint part. In this case, the length of the joint part(hereinafter, to be referred to as the joint length as appropriate) is the length including the seal part(i.e., the axial length from the distal end position of the distal-side tubular portionto the proximal end position of the seal part). The seal partwill be described in detail later.

31 2 31 21 31 21 21 31 The number of the first ribsis not necessarily limited, but in terms of improving the insertability as guides during the insertion of the joint partinto the plug hole H, it is preferable for the first ribsto be formed at three or more locations on the outer circumferential surface of the main tubular portion. For example, the number of the first ribsmay be suitably set, within a range of 4 to 10 locations on the outer circumferential surface of the main tubular portion, according to the outer diameter of the proximal end or distal end of the main tubular portion, the inner diameter of the plug hole H and the like, so as to obtain the desired insertability and rigidity. Similarly, the width and protruding height of the first ribsmay also be suitably set.

6 FIG. 2 12 11 12 13 131 22 2 12 12 12 20 4 131 13 4 131 As shown in, on the proximal side of the plug hole H, the joint partis fitted onto a high-voltage tower partthat protrudes from the coil main body part. The high-voltage tower partholds a high-voltage terminaland a resistortherein. The proximal-side tubular portionof the joint parthas the high-voltage tower partinserted thereinto from the distal end of the high-voltage tower part, so that the high-voltage tower partis inserted into the cylindrical holeand a proximal end of the electroconductive memberis brought into abutment with the resistor. Consequently, the high-voltage terminaland the electroconductive memberare electrically connected with each other via the resistor.

11 14 12 14 151 152 161 162 152 13 4 The coil main body parthas an electrically-insulative coil casearranged on the proximal side of the high-voltage tower part. In the coil case, there are accommodated: a primary coiland a secondary coilthat are arranged coaxially with each other; a central corearranged inside the coils; and an outer peripheral corearranged on the outer periphery of the coils. Consequently, a high voltage generated in the secondary coilcan be outputted from the high-voltage terminaland then applied to the ignition plug P via the electroconductive member.

4 FIG. 32 22 2 32 22 2 32 32 2 32 22 24 As shown in, the second ribs, each of which protrudes outward in the radial direction X, are formed respectively at a plurality of locations on the outer circumferential surface of the proximal-side tubular portionof the joint part. More particularly, in the present embodiment, eight second ribsare formed respectively at eight locations on the outer circumferential surface of the proximal-side tubular portionof the joint part. The second ribseach have a substantially trapezoidal cross-sectional shape, protrude in a radial fashion, and together form a gear-like external shape. The second ribsextend parallel to each other along the axis L of the joint part. Moreover, the second ribsare formed over the entire length from the proximal side to the distal side of the proximal-side tubular portion, i.e., to the proximal end position of the intermediate tubular portion.

3 FIG. 4 FIG. 5 FIG. 32 321 22 2 22 32 2 22 32 22 22 32 321 22 321 321 32 24 21 4 24 2 21 4 22 321 32 2 d d d d d d As shown in, each of the second ribshas, at a distal end thereof, a tapered portionthat slopes downward toward the distal side. Therefore, in a distal end part of the proximal-side tubular portion, the second rib diameter, which is the diameter of the imaginary circumscribing circle Cshown in, gradually decreases toward the distal side. In the proximal-side tubular portionexcluding the distal end part thereof, the second ribshave a gentle slope; and the second rib diameter has the maximum valueat the proximal end of the proximal-side tubular portion. It is preferable that the second ribshave a slope equal to the taper angle of the proximal-side half part Hso that the proximal-side tubular portioncomes into surface contact with the inner circumferential surface of the plug hole H on the proximal side. The slope of the second ribsat the tapered portionsthereof is greater than that at the proximal-side tubular portionon the proximal side of the tapered portions. Moreover, distal ends of the tapered portionsof the second ribsare connected with the intermediate tubular portion. Therefore, the minimum value dof the second rib diameter is greater than or equal to the outer diameterof the intermediate tubular portionshown in. That is, the following relationship is satisfied:>≥. In the distal end part of the proximal-side tubular portionwhere the tapered portionsof the second ribsare formed, the second rib diameter increases toward the proximal side, approaching the maximum value.

32 22 321 22 As above, each of the second ribsof the proximal-side tubular portionhas the tapered portionformed at the distal end thereof, so that the proximal-side tubular portionas a whole has a tapered shape that narrows toward the distal side, thereby improving the insertability.

32 22 32 32 22 32 2 2 2 2 2 1 4 1 11 3 d d d d d d It is preferable that the second ribsbe evenly arranged at substantially equal intervals in the circumferential direction on the outer circumferential surface of the proximal-side tubular portion. The protruding ends of the second ribsface the inner circumferential surface of the plug hole H, which is located outside the second ribsin the radial direction X, through a gap formed therebetween. The larger the gap, the more the insertability is improved. However, there is a risk of axial misalignment. Therefore, it is preferable that the inner circumferential surface of the proximal-side half part Hon the plug hole entrance side and the second ribsbe located close to each other with a slight gap, which is within a range that does not impair the insertability, formed therebetween. In this case, the second inner diameter Dat the proximal-side entrance part Hof the plug hole H and the maximum valueof the second rib diameter satisfy the relationship of D>(> D>≥>≥).

22 32 22 2 25 31 1 22 22 32 2 2 2 25 31 31 32 2 2 22 2 32 The axial length of the proximal-side tubular portionon which the second ribsare arranged is not necessarily limited; however, it is preferable to set the axial length of the proximal-side tubular portionaccording to the length of the joint partincluding the seal partso that the axial length of the first ribslocated astride the bend Hof the plug hole H becomes greater than the axial length of the proximal-side tubular portion. Specifically, in order to obtain the effect of axial alignment on the plug hole entrance side of the proximal-side half part Hof the plug hole H, the distal end position of the second ribsinserted into the proximal-side entrance part Hof the plug hole H may be set to, for example, a position within a range of 1% to 20% of the length of the joint partfrom the proximal end position of the joint part(i.e., the proximal end position of the seal part) according to the arrangement of the first ribsand the like. It is preferable to suitably set, within a range in which the axial length of the first ribscan be secured, the distal end position of the second ribsto a position of 5% or more of the length of the joint partfrom the proximal end position of the joint part. In this case, it will be possible to secure the length for which the proximal-side tubular portionmakes surface contact with the inner circumferential surface of the plug hole H in the vicinity of the proximal-side entrance part H, thereby enhancing the function of the second ribsas guides.

32 2 32 22 32 22 2 22 2 32 The number of the second ribsis not necessarily limited, but in terms of improving the insertability as guides during the insertion of the joint partinto the plug hole H, it is preferable for the second ribsto be formed at three or more locations on the outer circumferential surface of the proximal-side tubular portion. For example, the number of the second ribsmay be suitably set, within a range of 4 to 10 locations on the outer circumferential surface of the proximal-side tubular portion, according to the shape of the proximal-side half part Hof the plug hole H in which the proximal-side tubular portionis arranged, the inner diameter of the proximal-side entrance part Hof the plug hole H and the like, so as to obtain the desired insertability and rigidity. Similarly, the width and protruding height of the second ribsmay also be suitably set.

1 2 FIGS.and 25 2 11 25 22 2 2 25 22 2 2 11 1 11 2 25 25 2 25 As shown in, the seal partis arranged, on the proximal side of the plug hole H, between the proximal-side entrance part Hand the coil main body part. The seal partis formed of rubber, and is formed integrally with the proximal end of the proximal-side tubular portionof the joint part, constituting a part of the joint part. In this case, the seal partmay be formed so as to protrude, in a flange shape, outward in the radial direction X from the proximal end of the proximal-side tubular portionand thereby cover the proximal-side entrance part Hof the plug hole H. The proximal-side entrance part His formed, on the first surface Eof the cylinder head Ewhere the proximal end of the plug hole H opens, so as to protrude in annular shape from the first surface E. The proximal-side entrance part Hfunctions as a locking part that locks the seal part. A protruding end of the seal part, which is bent to have a L-shaped cross section, is locked to the proximal-side entrance part H, so that the proximal-side opening of the plug hole H can be sealed by the seal part.

11 141 14 141 142 13 11 1 141 11 13 13 11 141 12 25 25 In the coil main body part, there is formed a mounting flange partthat protrudes from a side of the coil case. Moreover, in the mounting flange part, there is formed a through-holethrough which a bolt is inserted. A support base partis formed, on the first surface Eof the cylinder head Ewhich faces the mounting flange part, to protrude from the first surface E. Furthermore, in the support base part, there is formed a threaded hole E. With above configuration, the coil main body partcan be fixed, by placing the mounting flange parton the support base part Eand fastening a bolt (not shown), to the proximal end of the plug hole H via the seal part; consequently, the plug hole H can be hermetically sealed by the seal part.

1 2 11 2 2 1 21 31 21 311 31 2 1 1 21 2 2 23 2 2 FIG. d The ignition coilmay be assembled to the plug hole H in, for example, the following way. First, as shown in, the joint part, whose proximal end is fitted to the coil main body part, is inserted from the proximal-side entrance part Hof the plug hole H toward the distal side into the plug hole H in which the ignition plug P is mounted. Specifically, the joint partis inserted coaxially with the axis Lof the distal-side half part Hof the plug hole H, with the first ribs, which are formed on the main tubular portion, functioning as guides. Moreover, with the tapered portionsformed respectively at the distal ends thereof, the first ribsare prevented from getting caught during the insertion of the joint partinto the plug hole H. In this case, the insertion force will not increase even if the difference between the maximum valueof the first rib diameter and the inner diameter Dof the distal-side half part Hof the plug hole H is reduced; moreover, the rigidity of the joint partis improved, thereby facilitating the axial alignment between the joint partand the plug hole H. Consequently, the distal-side tubular portionof the joint partcan have the ignition plug P coaxially inserted thereinto.

21 2 1 21 2 2 23 1 31 2 22 22 2 2 32 321 32 2 2 22 22 2 22 d Next, the main tubular portionof the joint partis further inserted toward the distal side of the plug hole H while being bent, at the bend Hof the plug hole H, along the bent shape of the plug hole H. Consequently, the main tubular portionof the joint partcan be bent and deformed such that: on the distal side of the joint part, the distal-side tubular portionis kept coaxial with the ignition plug P; and on the proximal side of the bend H, the axis L of the first ribsis kept coaxial with the axis Lof the proximal-side half part Hof the plug hole H. Then, on the proximal side of the plug hole H, the proximal-side tubular portionof the joint partis mounted into the proximal-side entrance part Hof the plug hole H, with the second ribsfunctioning as guides. In this case, by the tapered portionsformed respectively at the distal ends of the second ribs, the insertability is improved; and the difference between the maximum valueof the second rib diameter and the inner diameter Dof the proximal-side half part Hcan be reduced, thereby restricting the proximal-side tubular portionof the joint partto a coaxial position with the proximal-side half part H.

7 FIG. 7 FIG. 8 FIG. 8 FIG. 2 32 1 2 22 2 2 2 2 2 141 11 2 11 illustrates a first comparative example in which the joint parthas no second ribs, and has a constant diameter from a portion thereof facing the bend Hof the plug hole H to the proximal end thereof. With this configuration, it is difficult to carry out the axial alignment between the joint partand the proximal-side half part Hof the plug hole H when assembling the joint partto the proximal-side opening edge of the plug hole H while bending the joint partalong the bent shape of the plug hole H (e.g., in the direction indicated by the arrow in). Moreover, with this configuration, as shown in, the difference between the inner diameter Dof the proximal-side entrance part Hand the outer diameter of the joint partbecomes large. Consequently, when a mounting bolt B is tightened and fixed to the mounting flange partof the coil main body part, a rotational force acts (e.g., in the direction indicated by the arrow in) so that it becomes easy for axial misalignment of the joint partto occur. As a result, it becomes necessary to provide a rotation stopper or the like to suppress displacement of the coil main body part.

9 FIG. 9 FIG. 2 2 2 1 2 1 1 2 1 1 illustrates a second comparative example in which a portion of the joint partis thin-walled. With this configuration, the joint partcan be easily deformed along the bent shape of the plug hole H; however, upon the joint partbeing brought into contact with the bend Hof the plug hole H, the contact portion (e.g., the portion A shown in) of the joint partwith the bend Hmay become worn. For example, in a state of the ignition coilhaving been mounted to an engine, if the contact portion of the joint partis displaced due to vibration or the like while being kept in contact with the bend H, the thickness of the contact portion may gradually decrease due to wear, resulting in a decrease in the withstand voltage of the ignition coil.

2 31 1 32 2 2 32 2 2 1 In contrast, the joint partaccording to the present embodiment has the first ribsopposed to the bend Hof the plug hole H and the second ribsopposed to the proximal-side entrance part H. Consequently, it becomes possible to suppress axial misalignment over the entire length of the joint part. Moreover, with the second ribsarranged at the proximal-side entrance part H, it becomes possible to restrict the joint partto be coaxial with the plug hole H, thereby eliminating the need for a rotation stopper during the assembly of the ignition coilto the plug hole H.

31 32 2 31 1 2 2 31 1 21 1 Furthermore, with the first ribsand the second ribs, the rigidity of the joint partis improved so that even if the first ribsare brought into contact with the bend Hof the ignition hole H, displacement of the joint partdue to vibration or the like can be suppressed. Moreover, even if displacement of the joint partoccurs, only the first ribsextending in the axial direction make contact with the bend Hof the ignition hole H. Consequently, it becomes possible to prevent the thickness of the main body of the main tubular portionfrom being decreased due to wear; thus, it becomes possible to prevent the withstand voltage of the ignition coilfrom being lowered.

4 2 13 131 12 4 2 1 1 In the above-described first embodiment, the electroconductive memberarranged inside the joint partis constituted of a spring and electrically connected with the high-voltage terminalvia the resistorof the high-voltage tower part. However, the electroconductive membermay be constituted of any electroconductive member that can be bent and deformed together with the joint part. Moreover, in the above-described first embodiment, the ignition coilis applied to a vehicle engine. However, the ignition coilmay alternatively be applied to an internal combustion engine of a cogeneration system or the like. In addition, it should be noted that among the reference signs used in the first and subsequent embodiments, unless otherwise specified, the same reference signs as those used in the previous embodiment(s) designate the same components as those in the previous embodiment(s).

11 1 11 2 The present disclosure is not limited to the above-described embodiments, but can also be implemented through various modifications to the above-described embodiments without departing from the gist of the present disclosure. For example, the configuration of the coil main body partof the ignition coiland the connection structure of the coil main body partwith the joint partmay be suitably modified in various ways.

The following notes summarize the features of the present disclosure.

1 1 An ignition coil () configured to supply a high voltage to an ignition plug (P) arranged in a plug hole (H) having a bend (H), the ignition coil comprising:

11 2 a coil main body part () configured to be arranged at a proximal-side entrance part (H) of the plug hole, the proximal-side entrance part having an inner diameter greater than that of the bend; and

2 a joint part () formed of a tubular elastic body that is bendable and deformable, the join part having a proximal end mounted to the coil main body part and a distal end to be mounted to the ignition plug,

wherein:

31 21 the joint part has a plurality of first ribs () formed on an outer circumferential surface of a main tubular portion () of the joint part, each of the first ribs extending along an axis (L) of the joint part, the main tubular portion having a part thereof to be opposed to the bend of the plug hole;

the first ribs are arranged continuously, on both a distal side and a proximal side of the part of the main tubular portion which is to be opposed to the bend of the plug hole, toward both a distal end and a proximal end of the main tubular portion;

32 22 the joint part also has a plurality of second ribs () formed on an outer circumferential surface of a proximal-side tubular portion () of the joint part, each of the second ribs also extending along the axis of the joint part, the proximal-side tubular portion being located on a proximal side of the main tubular portion; and

1 1 2 2 2 c d c when viewed along the axis of the joint part, a maximum value d1 of a first rib diameter, which is represented by the diameter of an imaginary circumscribing circle (C) having its center () located on the axis and circumscribing tips of the first ribs, and a maximum valueof a second rib diameter, which is represented by the diameter of an imaginary circumscribing circle (C) having its center () located on

d d 2 1 the axis and circumscribing tips of the second ribs, satisfy the relationship of>.

The ignition coil according to the first note, wherein the first ribs are formed over an entire length of the main tubular portion and configured to be deformed, at the part of the main tubular portion which is to be opposed to the bend of the plug hole, into a shape along the bend of the plug hole.

311 The ignition coil according to the first or second note, wherein each of the first ribs has, at a distal end thereof, a tapered portion () where the first rib diameter decreases toward the distal side.

The ignition coil according to any one of the first to third notes, wherein the second ribs are arranged continuously from a proximal side to a distal side, so as to face a proximal-side end part of the plug hole which includes the proximal-side entrance part.

321 The ignition coil according to any one of the first to fourth notes, wherein each of the second ribs has, at a distal end thereof, a tapered portion () where the second rib diameter decreases toward the distal side.

The ignition coil according to any one of the first to fifth notes, wherein:

d d 1 1 1 1 the maximum valueof the first rib diameter and a first inner diameter D, which is the inner diameter of the plug hole at the bend, satisfy the relationship of D>; and

d 2 the maximum valueof the second rib diameter and a second inner

2 2 2 d diameter D, which is the inner diameter of the plug hole at the proximal-side entrance part, satisfy the relationship of D>.

The ignition coil according to any one of the first to sixth notes, wherein:

23 the joint part further has a straight-shaped distal-side tubular portion () formed on the distal side of the main tubular portion so as to be fitted onto a head portion of the ignition plug; and

d d d d d d 3 1 11 1 11 3 an outer diameterof the distal-side tubular portion and the maximum valueand a minimum valueof the first rib diameter satisfy the relationship of>≥.

The ignition coil according to the seventh note, wherein:

24 the joint part further has a straight-shaped intermediate tubular portion () formed between the main tubular portion and the proximal-side tubular portion; and

d d d d d d 4 2 21 2 21 4 an outer diameterof the intermediate tubular portion and the maximum valueand a minimum valueof the second rib diameter satisfy the relationship of>≥.

d d d d 3 4 4 3 The ignition coil according to the eighth note, wherein the outer diameterof the distal-side tubular portion and the outer diameterof the intermediate tubular portion satisfy the relationship of>.

While the present disclosure has been described pursuant to the above embodiments, it should be appreciated that the present disclosure is not limited to the embodiments and the structures. Instead, the present disclosure encompasses various modifications and changes within equivalent ranges. In addition, various combinations and modes are also included in the category and the scope of technical idea of the present disclosure.